Locks that are operated by keys today fall into several general classes. The only locks worth discussing from the point of view of high security are those where the keys can have a great many variations so that simply supplying a large assortment of keys is not practicable. Such locks, in general, employ mechanisms where the key sets up a set of elements, usually called tumblers, that may be small cylinders, pins, flat washers, sectors, or complete circles, and where each of such tumblers can be set into one of a plurality of positions. It follows, therefore, that if a key can set six tumblers, each of which can have ten positions, the number of combinations can become one million. In practice, such large numbers are not easily reached because of practical constraints, but this is the general theory.
The manner inwhich such locks are generally picked is that a suitable tool or tools are inserted into the passage for the key, and each tumbler is manipulated while the lock mechanism is under some forced constraint. By feeling the motion of a tumbler, it is possible to determine its correct position or, in some cases, one of several possible correct positions.
In order to make such locks difficult to pick, various expedients are resorted to. Tumblers are provided with fake notches, special shapes are used to make them difficult to move, a large number of tumblers are provided by making the key more elaborate as, for example, by cutting the key on both edges and providing two sets of tumblers, or by making the key slot with four sets of tumblers mounted at right angles, etc. There is a class of locks popular at the present time where pin tumblers are not only raised to their proper position but also rotated slightly by the key with each tumbler provided with an opening in its side into which a special sidebar fits when they are all in the correct positions, both axially and in rotation.
To the best of my knowledge, all such locks can be picked except that in the case of the best of them, this is difficult and requires great skill and is time consuming. As described in my U.S. Pat. No. 4,111,019, I have designed and built models of locks which so far have defied the efforts of some of the outstanding lock experts. This lock uses two sets of opposing tumblers which are set by a thin flat key bent into a wavy shape. The lock provides no space for a straight pick or a pick of any other shape except that of the correct key, and no tool thicker than the key has any chance of opening the lock. The lock does have the disadvantage in that the keys are not of the standard type and cannot be duplicated by existing key-cutting equipment.
In U.S. Pat. No. 3,172,283 also issued to me, I describe a combination lock that is probably impossible to defeat without X-raying the mechanism or physically damaging the lock as, for example, by drilling.
This present invention describes a lock system that uses any ordinary type of key, but which is proof against all methods of surreptitious entry that are known to me. The lock has the advantage that conventional key making and duplicating equipment may be used and also that the usual key mastering techniques can be employed, if desired.
An excellent overall description that treats the whole subject of locks is the recently published report of the National Bureau of Standards entitled "High Security Locking Devices: A State-of-the-Art Report," No. NBSIR 81-2233, issued January 1982.